1. Field of the Invention
This invention relates generally to seals between a housing and a rotatable shaft and, more particularly, to such seals in which a rotatable surface sealingly contacts a fixed surface.
2. Prior Art
Many industries require the use of machines in which a rotatable shaft is contained by a housing. The housing usually contains lubricated bearings and sometimes additional attachments to the shaft such as turbine blades or gears. There arc many types of seals provided between a shaft and a housing so as to prevent the leakage of lubricants from the housing and/or to prevent external contaminants from entering the housing along the shaft. In high speed operations of such rotating shaft mechanisms, contaminants to the internal lubricant result in increased wear, costly replacement of parts and, consequently, down time for the mechanism.
It is known to provide a scaling ring assembly comprising a first ring fixed to the housing and a second ring exterior to the housing and fixed to rotate with the shaft. Such an assembly is disclosed by U.S. Pat. No. 4,002,479, invented by David C. Orlowski and issued on May 10, 1977. Such seals, known as "labyrinth" seals, provide protection to internal parts by creating a labyrinth through which contaminants must pass to reach internal parts. During periods when the shaft is not rotating, labyrinth seals necessarily, by their nature, provide a path through which contaminants may reach internal parts. This failing has heretofore been accepted as the norm in exchange for satisfactory performance during rotation coupled with size considerations, case of installation and replacement (including the replacement of lip seals with labyrinth seals) and relatively low unit cost. Improvements in the art were made by Michael J. Ballard, the inventor herein, and disclosed in U.S. Pat. Nos. 4,484,754, 4,685,684 and 4,576,383. The Ballard patents also provide for additional protection created by the dynamics of the seal during rotation.
Prior art labyrinth seals do not provide a "positive" seal, that is, a constant surface to surface contact which prevents contaminants from entering a protected environment. Prior art positive seals include complex mechanical seals, such as the mechanical seal disclosed in U.S. Pat. No. 4,466,619 to Adams, as well as many others. Prior art mechanical seals utilize a stationary sealing face and a rotatable sealing face which are urged together to form a seal. The faces are manufactured from a hardened material which is polished, or "lapped", to a high degree of flatness, such that the surfaces provide a seal when urged together by springs or other resilient means. Mechanical seals occupy a large volume in order to accommodate the numerous complex parts required for the seal to operate. Further, the sealing surfaces must be lubricated and cooled, either by the working fluid contained by the seal or by a separate barrier fluid. Thus, mechanical seals are impractical for replacement of labyrinth seals, which occupy much less volume, and which are not lubricated by the working fluid or a barrier fluid.
However, it is highly desirable to provide a positive seal for protection of bearings and other internal parts while maintaining the size and relatively low cost of labyrinth seals.